Mast Cell Tryptase Induces Microglia Activation via Protease-activated Receptor 2 Signaling

Background: Mast cell tryptase can stimulate peripheral mononuclear cells activation to cause widespread inflammation. However, the influence of tryptase on microglia, the resident immune cells in the brain, remains uninvestigated. Since microglia plays a pivotal role in immune surveillance of CNS, we studied the effect of tryptase on microglia activation. Methods: Induction of microglia activation by tryptase was examined with primary cultured microglia. TNF-alpha and IL-6 was measured with a commercial ELISA kit. Intracellular ROS was determined by dichlorodihydrofluorescein oxidation. Mitochondrial membrane potential was assessed with the MitoProbe (TM) JC-1 assay kit. And MAPK and NF- kappa B phosphorylation were evaluated by Western blot. Results: We found that tryptase stimulated microglia activation and subsequently produced pro-inflammatory factors TNF-alpha, IL-6 and ROS. Inhibition of PAR-2 activation reduced tryptase-induced TNF-alpha, IL-6 and ROS production, and mitochondrial membrane potential loss in microglia. Among the three members of MAPK pathway, ERK and p38, but not JNK mediated tryptase-induced microglia activation. Inhibition of PAR-2 suppressed tryptase-induced ERK and p38 MAPK pathway activation in microglia. Tryptase also activated NF- kappa B within 30 min, and ammonium pyrrolidinedithiocarbamate, an inhibitor of NF- kappa B, reduced tryptase-induced TNF-alpha and IL-6 release. Conclusions: Our results suggest that tryptase can induce microglia activation and pro-inflammatory mediator release via PAR-2-MAPK-NF- kappa B signaling pathway, which will contribute to the development of microglia-mediated inflammation in brain. Copyright (C) 2012 S. Karger AG, Basel